1. Field of the Invention
The present invention generally relates to a method and device for correcting amplitude of a synchronizing signal of a composite video signal. More particularly, the invention relates to a method and device for correcting only the amplitude of a synchronizing signal to meet a standard without affecting video and color burst signals.
2. Description of the Related Art
Conventional systems utilize composite video signals which are used in various video apparatuses such as television sets or video tape recorders. The composite video signals are composed of a video signal such as a luminance signal and a chrominance signal, a color-burst signal such as a color synchronizing signal, and a synchronizing signal such as horizontal and vertical synchronizing signals.
Multiple video amplifiers and video switches are incorporated into modem video apparatuses. If the amplitude of a video signal is dynamically and significantly changed when a composite video signal passes through an amplifier, the amplitude of a synchronizing signal may be dynamically changed. If this occurs, then the amplitude of the synchronizing signal may be decreased depending on the state of video signal, and thus the composite video signal processing circuits in subsequent stages may fail to detect the synchronizing signal. In consequence, part of the screen image may be horizontally disordered or the whole screen image may momentarily swing in the vertical direction.
Two approaches are generally used to address the problem of a decreasing amplitude of a synchronizing signal. First, the whole composite video signal may be amplified using an amplifier in advance so that at least a required amplitude of a synchronizing signal can be secured even when the amplitude of the synchronizing signal dynamically decreases. Second, video circuits may be evaluated in a predetermined device configuration, and if no problem arises, it may be determined that the video circuits are acceptable. However, in the first approach, since the whole waveform is amplified, not only a synchronizing signal but also a video signal is amplified. In consequence, the reproducibility of an original video signal may be impaired, or gradation of white portions of a video image may be lost as a result that the amplified video signal is clipped by composite video signal processing circuits in subsequent stages. In the second approach, even though no problem was found in the device configuration used for the evaluation, problems may occur after shipping depending on user""s device configuration or the type of television monitor on the market.
In view of the foregoing and other problems of the conventional methods, it is, therefore, an object of the present invention to provide a method and a device for correcting amplitude of a synchronizing signal of a composite video signal without affecting other signal components.
It is also an object of the present invention to correct only the amplitude of a synchronizing signal to meet a standard without affecting video and color burst signals.
The present invention may include detecting a reference level which repetitively occurs at the same period as a synchronizing signal of the input composite video signal. A reference voltage may be generated corresponding to the amplitude of the synchronizing signal which meets a standard for the composite video signal. A DC voltage may be generating having a voltage level corresponding to a peak level of the synchronizing signal which meets the standard for the composite video signal based on the reference level and the reference voltage. The composite video signal and the DC voltage may be output in synchronism with the synchronizing signal extracted from the composite video signal.
The present invention may include a reference level detecting device for detecting a reference level which repetitively occurs at the same period as the synchronizing signal of the input composite video signal and a reference-voltage generating device for generating a reference voltage corresponding to an amplitude of the synchronizing signal which meets a standard for the input composite video signal. An arithmetic device generates a DC voltage having a voltage level corresponding to a peak level of the synchronizing signal which meets the standard for the input composite video signal based on the reference level and the reference voltage. An output switching device selectively outputs the composite video signal and the DC voltage in synchronism with the synchronizing signal extracted from the composite video signal.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description taken in conjunction with the annexed drawings, which disclose preferred embodiments of the invention.